Project Summary: Young gay, bisexual, and other men who have sex with men (MSM) are disproportionately affected by HIV. Despite this burden, most HIV prevention interventions target adult MSM (most of whom identify as gay) and heterosexual youth, creating an urgent need for interventions for gay and bisexual adolescents. Further, self- identified bisexual men, especially adolescents, have been neglected in research. This is a critical problem because: (1) there are as many, if not more, bisexual adolescent men than gay adolescent men; (2) bisexual adolescent men engage in several HIV risk behaviors more than their gay peers; (3) bisexual adolescent men are at increased risk for substance use?a robust risk factor for HIV; and (4) bisexual men face unique HIV prevention issues. Given that bisexual men are rarely included in research and most existing research on them focuses on ?behaviorally bisexual? adult men, little is known about factors that drive engagement in risk behavior among self-identified bisexual adolescent men. Attending to bisexual identity is critical to reducing HIV and substance use, because bisexuality is highly stigmatized and stigma-related stressors (e.g., concerns about disclosing one?s bisexual identity) impact sexual behavior, substance use, and healthcare utilization. Interventions are also more effective when tailored to populations, underscoring the need for an intervention for self-identified bisexual adolescent men. The goals of this study are to: (1) examine factors that drive engagement in HIV risk behavior and substance use among self-identified bisexual adolescent men; and (2) develop and pilot test a tailored HIV and substance use prevention intervention for this population. In Phase 1, interviews will be conducted with 60 diverse self-identified bisexual adolescent men ages 14-17 focused on sexual identity, sexual decision-making, substance use motivations, and intervention preferences/barriers. In Phase 2, a tailored intervention will be developed using findings from Phase 1. In Phase 3, feasibility, acceptability, and preliminary efficacy will be tested in a pilot randomized trial (N = 60) with a waitlist control and one-month follow-up. This award will provide the applicant with career development training in adolescent health, qualitative methods, and intervention development at Northwestern University?s Institute for Sexual and Gender Minority Health and Wellbeing?a well-resourced, rich intellectual environment for training scholars in sexual and gender minority health research. The training and research activities will facilitate the applicant?s transition to an independent investigator with a program of research focused on understanding and eliminating HIV and substance use disparities affecting bisexual men. In sum, self-identified bisexual adolescent men are at increased risk for HIV and substance use, but little is known about factors that drive their engagement in risk behavior. By focusing on self-identified bisexual adolescent men?an underrepresented, health disparity population?this study can identify prevention targets and reduce disparities in HIV and substance use.